As the only second-order inviscid invariant in three-dimensional turbulence except for the kinetic energy, helicity is crucial in the dynamics of turbulence. Rotating flows are often accompanied by high helicity in natural and engineering fields. Until recently, the spectral analyses of helicity are restricted to the topic of homogeneous isotropic turbulence.
The Numerical Simulation Group of Aerospace Vehicle Flow of the Institute of Mechanics in the Chinese Academy of Sciences recently introduced helicity into rotating turbulence and studied the dual cascades of energy and helicity.
The study was published in the Journal of Fluid Mechanics on Aug. 3.
They systematically analyzed the conservation and symmetry of energy and helicity transfers. A new expression of spectral helicity transfer is proposed, accompanied by the relations with classical expressions. The helicity has been found to inhibit the rotation-induced inverse cascade of energy. New physical mechanisms such as helicity chiral polarization were discovered in this study as well.
“Our work deepens the cognition of coupling mechanisms of helicity and rotation in turbulence and successfully expands spectral helicity analyses into complex turbulence,” said Yu, corresponding author of the study.
This work was supported by the National Key Research and Development Program of China (No. 2019YFA0405300 and No. 2020YFA0711800) and NSFC Projects (No. 91852203 and No. 12072349).
Fig.1. Vortex structures (a) without rotation and helicity; (b) without helicity but with rotation; (c) with rotation and maximum helicity; (d) with weak rotation and maximum helicity.
Institute of Mechanics, Chinese Aademy of Siences
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